Powder X-ray diffraction (XRD) is a well-known technique for analysis of crystalline materials. Powder XRD methods are usually applied in an angle-dispersive mode (ADXRD). In ADXRD, an X-ray beam with, ideally, a single wavelength λ is diffracted by a sample through a range of distinct scattering angles 2θ, according to the Bragg equation:λ=2d sin θ  (1)
The sample is powdered, so that the crystallites within the beam can generally be assumed to be randomly oriented in all directions. The derived set of crystal d-spacings, uniquely characteristic of each mineral phase, is used for phase identification, quantification and structural analysis, amongst other purposes. Energy-dispersive X-ray diffraction (EDXRD) is an alternative application of the Bragg equation. In EDXRD one fixes the scattering angle and scans the X-ray wavelength (equivalently, the X-ray energy). This method can also be implemented without scanning the X-ray wavelength: a broadband X-ray source, such as an X-ray tube, can be used together with an energy-resolving detector.
Both ADXRD and EDXRD have their particular benefits and drawbacks, and find application in different fields. In both techniques, however, X-ray diffraction is sensitive to the morphology of the sample under investigation. As a consequence of this sensitivity, it is difficult to analyse unprepared samples using the conventional techniques. For example, in a geological context, it is difficult to analyse whole rock samples. Rather, a uniform presentation of samples in powder form is required. Therefore the known techniques have limitations on their application, particularly in the field. Samples that are precious and must not be damaged, for example some archaeological artefacts, present difficulties to the powder XRD techniques, for obvious reasons.